If you access tiles (read or write) that are NULL-mapped, you get undefined behavior, which includes device-removed. Apps can map all tiles to a single "default" tile to avoid this condition.

D3D11_TILED_RESOURCES_TIER_2

Tier_2 tiled resources are supported.

Superset of Tier_1 functionality, which includes this additional support:

On Tier_1, if the size of a texture mipmap level is an integer multiple of the standard tile shape for its format, it is guaranteed to be nonpacked. On Tier_2, this guarantee is expanded to include mipmap levels whose size is at least one standard tile shape.
For more info, see D3D11_PACKED_MIP_DESC.

Shader instructions are available for clamping level-of-detail (LOD) and for obtaining status about the shader operation. For info about one of these shader instructions, see Sample(S,float,int,float,uint).

Reading from NULL-mapped tiles treat that sampled value as zero. Writes to NULL-mapped tiles are discarded.

D3D11_TILED_RESOURCES_TIER_3

Tier_3 tiled resources are supported.

Superset of Tier_2 functionality, Tier 3 is essentially Tier 2 but with the additional support of Texture3D for Tiled Resources.